CN115386366B - Sulfur quantum dot with simulated oxidase activity and high fluorescence quantum yield as well as preparation and application thereof - Google Patents

Sulfur quantum dot with simulated oxidase activity and high fluorescence quantum yield as well as preparation and application thereof Download PDF

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CN115386366B
CN115386366B CN202211099763.7A CN202211099763A CN115386366B CN 115386366 B CN115386366 B CN 115386366B CN 202211099763 A CN202211099763 A CN 202211099763A CN 115386366 B CN115386366 B CN 115386366B
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sqds
oxidase activity
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郭红瑞
王显祥
谢跃
左之才
郭海
刘心悦
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Sichuan Agricultural University
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Abstract

The invention discloses a sulfur quantum dot with high fluorescence quantum yield and simulated oxidase activity, and preparation and application thereof, wherein the preparation method comprises the following steps: mixing sublimed sulfur, sodium hydroxide, polyethylene glycol 400 and water, and heating and refluxing to obtain solution A; adding ferrate, mixing, and reacting at the same temperature to obtain solution B; taking supernatant liquid of the solution B, and marking the supernatant liquid as solution C; taking H 2 O 2 Mixing with the C solution, and etching by hydrogen peroxide to generate the sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which are marked as SQDs. The invention solves the problems of curative effect loss and pathogenic bacteria drug resistance formation caused by long-term use of antibiotics, and provides a novel method for detecting folic acid, which is simple and rapid and has high specificity. SQDs of the invention have oxidationThe enzyme activity shows excellent inhibition capability to typical pathogenic multi-drug resistant escherichia coli and methicillin-resistant staphylococcus aureus.

Description

Sulfur quantum dot with simulated oxidase activity and high fluorescence quantum yield as well as preparation and application thereof
Technical Field
The invention relates to a quantum dot, in particular to a sulfur quantum dot with simulated oxidase activity and high fluorescence quantum yield, and preparation and application thereof.
Background
Folic Acid (FA) is an important water-soluble vitamin B having various functions in the human body, such as acquisition, transport, and enzyme treatment of carbon units involved in amino acid and nucleic acid metabolism, and is an essential substance for cell growth and reproduction. But is usually provided by diet because it cannot be synthesized by the human body. The normal level of FA in serum is between 7 and 42nM, and the lack can lead to a number of diseases such as fetal neural tube defects, cardiovascular disease, megaloblastic anemia, etc. There are studies reporting that the generation of cancer is associated with FA at a low level as well. Therefore, it is very important to develop an accurate analytical technique for detecting FA. Quantum Dots (QDs) are an attractive fluorescent probe due to their size-tunable emission characteristics, narrow emission spectra, and high photoluminescence quantum yields (PLQY), and have been explored for the detection of various biomolecules. But the use of sulfur quantum dots to determine FA has not been reported.
In the current problem of gram bacterial infection, which is one of the global public health problems, the health of human beings is seriously threatened, and millions of people die each year due to the infection of drug-resistant bacteria. Since the discovery of penicillin, antibiotics have been powerful weapons for human treatment of disease caused by infection with pathogenic microorganisms, and they inhibit cell wall synthesis and damage to cell membranes, inhibit DNA and RNA synthesis, etc., thereby interfering with the basic physiological processes of bacteria. However, bacteria can develop resistance through gene mutation or transmit resistance to other strains through plasmids, and the occurrence of drug-resistant strains is caused by the long-term overuse of antibiotics, so that the treatment effect of the traditional antibiotics is reduced, even if the curative effect is lost in many cases, the formation of pathogenic bacteria resistance is increasingly serious. Therefore, it is extremely necessary to explore and develop novel antibacterial agents with high antibacterial efficiency. Sulfur quantum dots are attracting attention as a new potential broad-spectrum antibiotic due to the inherent antimicrobial activity of elemental sulfur and the broad-spectrum antimicrobial activity, non-resistance and high efficiency of nanomaterials. Although the sulfur quantum dots have wide application in the fields of biological sensing, food analysis, detection, photoelectric devices and the like, the application of the sulfur quantum dots in bacteriostasis is reported recently.
Disclosure of Invention
The invention aims to provide a sulfur quantum dot with high fluorescence quantum yield and simulated oxidase activity, and preparation and application thereof, solve the problems of curative effect loss and pathogenic bacteria drug resistance formation caused by long-term use of antibiotics, and provide a novel method for detecting folic acid, which is simple and rapid and has high specificity for folic acid.
In order to achieve the above object, the present invention provides a method for preparing sulfur quantum dots with high fluorescence quantum yield having a simulated oxidase activity, the method comprising:
(1) Mixing sublimed sulfur, sodium hydroxide, polyethylene glycol 400 and water, and heating and refluxing to obtain solution A;
(2) Mixing the solution A prepared in the step (1) with ferrate, and reacting at the same temperature as in the step (1) to prepare solution B;
(3) Taking the supernatant liquid of the liquid B prepared in the step (2) and marking the supernatant liquid as liquid C;
(4) Mixing the C solution and H in the step (2) 2 O 2 Mixing at room temperature, and etching by hydrogen peroxide to generate sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which are marked as SQDs.
Preferably, the mass volume ratio of the sublimed sulfur, the sodium hydroxide, the polyethylene glycol 400 and the water is 0.7g:2g:1.5mL:25mL; said H 2 O 2 The concentration of the solution C and H is 1.6-6.5 mM 2 O 2 Is equal in volume.
More preferably, said H 2 O 2 Is 4mM.
Preferably, the mass ratio of sublimated sulfur to ferrate is 21.875:0.151.
preferably, the temperature of the heated reflux is 70 ℃.
The invention provides a sulfur quantum dot prepared by the preparation method. The sulfur quantum dot emits blue fluorescence under 370nm excitation, and the fluorescence emission peak is located at 450nm; the sulfur quantum dots are spherical, and the particle size is 20-80 nm.
The invention provides an application of sulfur quantum dots in preparing an antibacterial agent for inhibiting drug-resistant escherichia coli and/or methicillin-resistant staphylococcus aureus.
The invention provides an application of the sulfur quantum dot in detecting folic acid in non-diagnosis.
The invention provides a method for detecting folic acid in non-diagnosis by using the sulfur quantum dot, which comprises the following steps:
and adding the sulfur quantum dots into a sample to be detected, reacting at pH of 2-11, and measuring the fluorescence intensity of the reaction liquid at 450 nm.
Preferably, the pH is 7-11, and the reaction time is 1-10 minutes.
The high fluorescence quantum yield sulfur quantum dot with the simulated oxidase activity, and the preparation and the application thereof solve the problems of curative effect loss and pathogenic bacteria drug resistance formation caused by long-term use of antibiotics, and provide a novel method for detecting folic acid, which has the following advantages:
(1) The SQDs provided by the invention have fluorescence stability at pH of 2-10 or at temperature of 20-60 ℃ or at NaCl concentration of 0-1.0M.
(2) The SQDs provided by the invention have extremely high fluorescence quantum yield which reaches 35.24%.
(3) The SQDs provided by the invention can be used as a fluorescent probe for directly detecting folic acid, and the method is simple and rapid, has high specificity and has the detection limit as low as 9.16 mu M.
(4) The SQDs provided by the invention are sulfur quantum dot materials with oxidase activity, the optimal pH is 3, and the optimal temperature is 40 ℃.
(5) The SQDs provided by the invention have excellent inhibition capability on typical pathogenic multi-drug resistant escherichia coli and methicillin-resistant staphylococcus aureus, and particularly have the material concentration of less than or equal to 0.1mg/mL, and can effectively inhibit the growth of drug-resistant bacteria.
Drawings
FIG. 1 is a graph showing the optimum amount of potassium ferrate synthesized by SQDs prepared in examples 1-7 of the present invention.
FIG. 2 shows the synthesis H of SQDs prepared in examples 1, 8-13 of the present invention 2 O 2 An optimization graph.
FIG. 3 is a HRTEM diagram of SQDs prepared in example 1 of the present invention.
FIG. 4 is a graph showing the particle size distribution of SQDs produced in example 1 of the present invention.
FIG. 5 is a graph showing the optical properties of SQDs prepared in example 1 of the present invention.
FIG. 6 is a graph showing the excitation dependence of SQDs produced in example 1 of the present invention.
FIG. 7 is a XPS total spectrum of SQDs prepared in example 1 of the present invention.
FIG. 8 is an XPS fine spectrum of the SQDs element of example 1 of the present invention.
FIG. 9 is a FTIR spectrum of SQDs prepared in example 1 of the present invention.
FIG. 10 is a graph showing the pH stability of SQDs prepared in example 1 of the present invention.
FIG. 11 is a graph showing the temperature stability of SQDs prepared in example 1 of the present invention.
FIG. 12 is a graph showing the salt stability of SQDs prepared in example 1 of the present invention.
FIG. 13 is a pH optimum of SQDs detection FA prepared in example 1 of the present invention.
FIG. 14 is a time-optimized graph of the SQDs detection FA prepared in example 1 of the present invention.
FIG. 15 shows fluorescence specificity of SQDs detection FA prepared in example 1 of the present invention.
FIG. 16 is a fluorescence spectrum of SQDs detection FA prepared in example 1 of the present invention.
FIG. 17A standard graph of the SQDs detection FA prepared in example 1 of the present invention, in which the FA concentration is on the abscissa and the fluorescence intensity F 0 and/F is the ordinate.
FIG. 18 is a graph of simulated oxidative enzymatic optima for SQDs prepared in example 1 of the present invention, wherein A is the relative activity detected at different pH values; b is the relative activity detected at different temperatures.
FIG. 19 is a graph of bacterial viability of different concentrations of SQDs material on two resistant bacteria, wherein A is the percent survival of methicillin-resistant Staphylococcus aureus; b is the survival percentage of multi-drug resistant escherichia coli.
FIG. 20 shows the OD of the bacterial suspension after treatment with different material groups 600 Values.
FIG. 21 is a diagram of a petri dish after treatment with different material groups, wherein A is multi-drug resistant E.coli and C is multi-drug resistant E.coli +SQDs; b is multi-drug resistant escherichia coli, D is methicillin-resistant staphylococcus aureus+SQDs.
FIG. 22 is a fluorescence comparison of SQDs prepared in example 1 of the present invention with quinine sulfate.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The tablets and culture media used in the following experimental examples of the present invention are as follows:
tablet a is 0.4mg,31 tablets/box, national drug standard H20003143, changzhou pharmaceutical factory Co., ltd;
tablet b is 0.4mg,100 tablets/box, national drug standard H36020872, jiangxi pharmaceutical Co., ltd;
tablet c is 0.4mg,93 tablets/box, national drug standard H20044917, jiangsu Ling pharmaceutical Co., ltd;
tablet d is 0.5mg,100 tablets/box, national drug standard H62020684, gansu blue pharmaceutical industry Co., ltd;
the culture medium is LB nutrient agar with the specification of 250g, which is Qingdao Haibo biotechnology Co.
Example 1
A method of preparing a high fluorescence quantum yield sulfur quantum dot having a simulated oxidase activity, the method comprising:
(1) Firstly, mixing 0.7g of sublimed sulfur, 2g of sodium hydroxide, 1.5mL of polyethylene glycol 400 and 25mL of distilled water, and refluxing for 4 hours at 70 ℃ to obtain solution A;
(2) Mixing 25mg of potassium ferrate in the solution A prepared in the step (1) and continuously maintaining the original reaction condition for reaction for 1h to obtain a solution B;
(3) The solution B obtained in the step (2) was centrifuged at 3500rpm for 5 minutes to leave a supernatant, which was designated as solution C (25 mL).
(4) Mixing the C solution in the step (2) with 4mMH 2 O 2 (25 mL) an equal volume of the mixture was further etched to give SQDs.
Example 2
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
the mass of potassium ferrate in step (2) is 2.5mg.
Example 3
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
the mass of potassium ferrate in the step (2) is 5.0mg.
Example 4
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
the mass of the potassium ferrate in the step (2) is 12.5mg.
Example 5
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
the mass of potassium ferrate in step (2) was 37.5mg.
Example 6
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
the mass of potassium ferrate in the step (2) is 50.0mg.
Example 7
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
the mass of potassium ferrate in step (2) is 62.5mg.
Example 8
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
h in step (4) 2 O 2 Is 1.6mM.
Example 9
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
h in step (4) 2 O 2 Is 2.4mM.
Example 10
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
h in step (4) 2 O 2 Is 3.2mM.
Example 11
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
h in step (4) 2 O 2 Is 4.9mM.
Example 12
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
h in step (4) 2 O 2 Is 5.7mM.
Example 13
A method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which is basically the same as in example 1, except that:
h in step (4) 2 O 2 Is 6.5mM.
As shown in FIG. 1, the synthetic potassium ferrate doping amount optimization diagrams of the SQDs prepared in examples 1 to 7 of the present invention; as shown in FIG. 2, the SQDs prepared in examples 1 and 8 to 13 of the present invention were synthesized to form H 2 O 2 An optimization graph. As can be seen from FIGS. 1-2, the optimum amount of potassium ferrate is 25mg, H is added 2 O 2 The optimal concentration of (2) is 4mM.
Experimental example 1 SQDs prepared in example 1 were subjected to HRTEM, XPS and FTIR characterization
As shown in FIG. 3, a TEM image of SQDs prepared in example 1. From FIG. 3, it can be seen that the SQDs after preparation are spherical and well dispersed.
As shown in FIG. 4, the particle size distribution of SQDs prepared in example 1 was shown. The average diameter was found to be 55nm as seen in FIG. 4.
As shown in FIG. 5, the optical properties of the SQDs prepared in example 1 are shown. As seen in FIG. 5, the SQDs have an absorption peak at 220nm, and under irradiation of ultraviolet rays at 370nm, the SQDs fluoresce bright blue at 450 nm.
As shown in FIG. 6, the excitation dependence of SQDs prepared in example 1 is shown. From fig. 6, it is shown that the peak position of the emission wavelength of SQDs is unchanged at different excitation wavelengths.
As shown in FIG. 7, the XPS total spectrum of SQDs prepared in example 1. The XPS spectrum shown by fig. 7 shows that SQD consists mainly of C, O and S.
As shown in FIG. 8, the S-element XPS-fine spectrum of SQDs prepared in example 1. As shown in FIG. 8, the key element S in SQDs shows peaks at 162.28eV and 164.58eV, which are the peaks corresponding to atomic sulfur, thus indicating successful synthesis of SQDs.
As shown in FIG. 9, the FTIR spectra of SQDs prepared in example 1. From FIG. 9, 1143cm -1 、833cm -1 And 623cm -1 The stretching vibrations of (a) are derived from the C-O bond, the S-O bond and the S-S bond, respectively, which confirm the successful synthesis of SQDs and further confirm the XPS result.
Thus, as can be seen from FIGS. 7-9, the Sulfur Quantum Dots (SQDs) prepared in example 1 were characterized by XPS and FTIR, and it can be seen that ferrate and hydrogen peroxide are used as strong oxidants, and the sulfur dots were successfully etched as sulfur quantum dots with continuous auxiliary precipitation.
Experimental example 2 stability test of SQDs prepared in example 1
At room temperature, adding 0.9ml of buffer solution with pH value of 2, 3, 4, 5, 6, 7, 8, 9 or 10 and 0.1ml of LSQDs into 2ml of polyethylene plastic pipe, uniformly mixing, pouring into a quartz cuvette for measuring fluorescence intensity after thermostatic water bath at 25 ℃ for 1min to verify the influence of pH on the fluorescence intensity of SQDs; similarly, under the optimal pH condition, 0.9mL of buffer solution with the optimal pH and 0.1mL of LSQDs are added into 2mL of polyethylene plastic pipe, the reaction system is reacted for 1min in water baths (20, 30, 40, 50 and 60 ℃) with different temperatures, and the reaction system is poured into a quartz cuvette to measure the fluorescence intensity so as to verify the influence of the temperature on the fluorescence intensity of the SQDs; with the optimal temperature and pH maintained, 0.8mL of the buffer solution with the optimal pH and 0.1mL of NaCl solution (0-1M) with different concentrations are added into 2mL of polyethylene plastic pipes, and the reaction is carried out for 1min, and poured into a quartz cuvette to measure the fluorescence intensity so as to verify the influence of the salt concentration on the fluorescence intensity of SQDs.
As shown in FIG. 10, the pH stability profile of SQDs prepared in example 1. From fig. 10, it is derived that the normalized fluorescence intensity of the SQD remains substantially stable when the pH value is changed from 2 to 10, which means that the SQD exhibits excellent optical stability even under extreme pH conditions.
As shown in FIG. 11, the temperature stability profile of SQDs prepared in example 1. As seen from FIG. 11, the fluorescence intensity slightly decreased with increasing temperature (20 ℃ C. To 60 ℃ C.), but remained generally stable, so that the normalized fluorescence intensity of the SQD was less affected by temperature.
As shown in FIG. 12, the salt stability profile of SQDs prepared in example 1. As can be seen from fig. 12, the fluorescence intensity of SQDs remained substantially stable when the NaCl concentration was increased from 0 to 1.0M, which suggests that SQDs have a good salt-resistant effect, demonstrating excellent fluorescence stability of SQDs.
Thus, as can be seen from FIGS. 10 to 12, the Sulfur Quantum Dots (SQDs) prepared in example 1 have good stability.
Experimental example 3 SQDs detection of folic acid prepared in example 1
The sulfur quantum dots prepared by the preparation method of example 1 detect folic acid, and the method comprises the following steps:
(1) Determination of optimal reaction conditions in systems where SQDs detect FA concentration:
buffer solutions (acetic acid-sodium acetate buffer) and 1 mfa solutions (prepared by dissolving FA in aqueous sodium hydroxide) were prepared at ph=3 to 11. 0.8mL of each buffer solution with different pH values, 0.1mL of LSQDs and 0.1mL of LFA solution are added into 2mL of polyethylene plastic pipe, after being uniformly mixed, the mixture is poured into a quartz cuvette for measuring fluorescence emission peak at 450nm after being subjected to constant temperature water bath at 25 ℃ for 1min, and the optimal reaction pH for detecting FA is determined.
As shown in FIG. 13, the SQDs detection FA prepared in example 1 has a pH optimum. As is clear from FIG. 13, the pH of the optimal reaction for detecting folic acid is 7 to 11.
0.8mL of buffer solution with the optimal pH value (pH value is 11) determined by the experiment is added into 2mL of polyethylene plastic pipe, 0.1mL of LSQDs and 0.1mL of LFA solution are uniformly mixed, the mixture is respectively subjected to constant temperature water bath for 1-10 min, poured into a quartz cuvette for measuring the fluorescence intensity at 450nm, and the optimal reaction time is determined according to the result.
As shown in FIG. 14, the SQDs detection FA prepared in example 1 is time optimized. As is clear from FIG. 14, the detection reaction time was substantially stable from 1 to 10 minutes.
(2) Specificity experiment for detecting FA by using SQDs as fluorescent probe
Other substances (folic acid, starch, magnesium stearate, lactose, low-substituted hydroxypropyl cellulose, microcrystalline cellulose, cysteine, ascorbic acid and the like) existing in the substances to be detected are selected for specificity test, and a 1mL system is constructed: 0.9mL of SQDs+0.1mL of the substance to be detected, 5mM of the substance to be detected, fluorescence detection is carried out, and the results are compared, a substance with specificity (folic acid) is selected for further determination of detection limit, and a standard curve is established.
As shown in FIG. 15, the SQDs prepared in example 1 detect fluorescence specificity of FA. As can be seen from FIG. 11, only folic acid can quench the fluorescence intensity of SQDs, and thus high specificity of detection of Folic Acid (FA) can be achieved by this fluorescence characteristic.
As shown in FIG. 16, the SQDs detection FA prepared in example 1 has a fluorescence spectrum. From FIG. 16, it is seen that the fluorescence intensity corresponding to SQDs gradually decreases as the amount of folic acid added increases.
(3) SQDs as fluorescent probes to detect FA and establish a standard curve
Under optimal reaction conditions (ph=11), SQDs were added with FA at different concentrations, and the fluorescence intensity F of the reaction solution was measured at 450 nm.
As shown in FIG. 17, the SQDs detection FA prepared in example 1 has a standard curve chart. Wherein the FA concentration is on the abscissa, and the fluorescence intensity F 0 /F(F 0 : sample group after folic acid addition, F: blank group without folic acid) is taken as an ordinate to obtain a detection FA standard curve. As can be seen from FIG. 17, the ratio of the folic acid concentration to the fluorescence intensity before and after addition of folic acid has a good linear relationship in the range of 10 to 350. Mu.M, and the detection limit is as low as 9.16. Mu.M.
Experimental example 4 evaluation of applicability of the SQDs Folic acid detection method prepared in example 1
In order to evaluate the applicability of the folic acid detection method provided in experimental example 3 of the present invention, the folic acid in the actual drug sample was recovered by labeling. Under the optimal conditions of each parameter (pH is 7-11, and the reaction time is 1-10 min), the concentration of folic acid medicines with different brands, different auxiliary materials and specifications is detected. The test results are shown in Table 1:
table 1 shows the results of the standard recovery method for determining the folic acid content of the actual medicines, and the recovery rate of the folic acid is determined to be between 96.19% and 106.25%. The result shows that the method can be used for measuring folic acid in actual samples, and has a lower concentration range than that of the folic acid detected by quantum dots reported in the prior literature.
Experimental example 5 simulation of the oxidase Activity of SQDs prepared in example 1
The (SQDs) prepared in example 1 was subjected to a simulated oxidase activity study: the optimal conditions for the materials to mimic the enzyme activity were explored, and a 2mL reaction system (1.8 mL of 0.1M acetic acid-sodium acetate buffer, 0.1mL of QDs, and 0.1mL of TMB at 5 mM) was set using TMB as a chromogenic substrate. The single variable was set, and the optimal pH (pH 3, determined by absorbance at 652 nm) for the enzymatic activity of the material at room temperature was determined, and then the optimal temperature (40 ℃ C., absorbance at 652nm at different temperatures) at the optimal pH was determined. Obtaining the optimal condition of the enzymatic reaction. The enzymatic kinetics were tested at the optimal reaction temperature and pH. The apparent kinetic parameters were then according to Michaelis-Menten equation:
V=V max *[S]/(K m +[S])
wherein V is the initial velocity, V max Is the maximum reaction speed [ S ]]For substrate concentration, K m Is a Mie constant.
As shown in FIG. 18, the simulated oxidative enzymatic optima for SQDs prepared in example 1, wherein A is the relative activity detected at different pH values; b is the relative activity detected at different temperatures. From FIG. 18, it is found that the SQDs-simulated oxidase activity has an optimum pH of 3 and an optimum temperature of 40 ℃.
Experimental example 6 evaluation of bacteriostatic ability of SQDs prepared in example 1
Sulfur Quantum Dots (SQDs) prepared in example 1 were used to inhibit the growth of drug-resistant bacteria, and the bacteriostatic ability was evaluated, which method comprises:
(1) Preparation of bacterial liquid
Transferring the drug-resistant bacteria inoculated on LB agar plate into LB broth, standing for shaking culture for 12 hr, diluting with sterile double distilled water, and diluting to optical density of 0.1 (OD) at 600nm 600 =0.1)。
(2) Determination of Minimum Inhibitory Concentration (MIC) of SQDs
MIC determination by micro broth dilution, 10mg/mL, 1.0mg/mL, 10 were added sequentially to wells 1 to 7 -1 mg/mL、10 -2 mg/mL、10 -3 mg/mL、10 -4 mg/mL、10 -5 The SQDs of mg/mL were 100. Mu.L, and then 100. Mu.L of the above-mentioned concentration bacterial suspension was added to each well to establish a 200. Mu.L system, and mixed well, three groups of each concentration were performed in parallel. 200 mu L of culture medium is used as a blank control, 100 mu L of bacterial liquid and 100 mu L of culture medium are used as positive control, and 100 mu L of culture medium and 100 mu LSQDs are used as material color control. Placing the 96-well plate on a micro-oscillator to vibrate for a little time, so that the liquid in the 96-well plate is fully and uniformly mixed, and placing the mixture into a constant temperature incubator at 37 ℃ for culturing for 24 hours. Determination of OD by means of an enzyme-labeled instrument 600 The value was judged to be MIC at the lowest drug concentration that could inhibit the growth of pathogenic bacteria in the medium when cultured in vitro.
As shown in fig. 19, the bacterial viability graph of different concentrations of SQDs material on two drug-resistant bacteria, wherein a is the percent survival of methicillin-resistant staphylococcus aureus; b is the survival percentage of multi-drug resistant escherichia coli. As shown in FIG. 19, the growth of drug-resistant bacteria can be effectively inhibited when the material concentration is less than or equal to 0.1 mg/mL.
(3) Evaluation of antibacterial Activity of SQDs
Antibacterial activity of SQDs was evaluated using multi-drug resistant E.coli and methicillin-resistant Staphylococcus aureus as models. The multi-drug resistant escherichia coli/methicillin-resistant staphylococcus aureus is divided into 2 groups, namely (1) 100 mu L of bacterial liquid and 100 mu L of physiological saline (CK); (2) 100. Mu.L of bacterial liquid+100. Mu.LSQDs. Each group of treated bacterial suspensions was incubated at 37℃for 6h to determine the Optical Density (OD) at 600nm 600 )。
As shown in FIG. 20, the bacterial suspensions OD after treatment with different material groups 600 Values. OD (optical density) 600 Represents the optical density value of the bacteria, i.e. the greater the bacterial density at an absorbance of 600nm, the corresponding OD 600 The larger the value; whereas the smaller. As seen in FIG. 20, the optical density values were greatly reduced after SQDs treatment.
The bacteriostatic activity of SQDs was further examined by plate counting against a medium without any bacteria: each group of multi-drug resistant escherichia coli/methicillin-resistant staphylococcus aureus suspension is coated on a solid culture medium, and is cultured for 12-16 hours at 37 ℃, and then the relative viability of the bacteria is measured by observing and counting the colony number.
As shown in fig. 21, a culture dish diagram after treatment of different material groups, wherein a is multi-drug resistant escherichia coli, and C is multi-drug resistant escherichia coli+sqds; b is multi-drug resistant escherichia coli, D is methicillin-resistant staphylococcus aureus+SQDs. It is apparent from FIG. 21 that SQDs have excellent antibacterial effect against both drug-resistant bacteria.
From the results of FIGS. 19-21, it can be seen that SODs material has good inhibitory effect on the growth of both resistant bacteria.
Experimental example 7 determination of fluorescence Quantum yield of SQDs prepared in example 1
The fluorescence Quantum Yield (QY) of the sulfur quantum dots SQDs prepared in example 1 was determined with quinine sulfate dissolved in 0.1M sulfuric acid as reference (excitation at 360nm wavelength, QY of 0.546). Quinine sulfate and OD values of the sample were measured on a water basis, noting OD values less than 0.05; fluorescence spectra of quinine sulfate and SQDs solutions were obtained at 360nm wavelength, and then QY of SQDs was calculated by the following formula:
wherein Q represents fluorescence quantum yield, I represents integrated area of fluorescence emission peak, OD represents ultraviolet absorption value (limit OD < 0.05), n represents refractive index of solution, and 1 is taken; subscript R represents quinine sulfate reference, and x represents the tested sample SQDs.
Carrying out data acquisition:
as shown in FIG. 22, the fluorescence of SQDs prepared in example 1 versus quinine sulfate is shown. From fig. 22, the photo quantum yield of the SQD prepared in example 1 was 35.24% from quinine sulfate as a reference solution.
While the present invention has been described in detail through the foregoing description of the preferred embodiment, it should be understood that the foregoing description is not to be considered as limiting the invention. Many modifications and substitutions of the present invention will become apparent to those of ordinary skill in the art upon reading the foregoing. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims (10)

1. A method for preparing a high fluorescence quantum yield sulfur quantum dot with simulated oxidase activity, comprising:
(1) Mixing sublimed sulfur, sodium hydroxide, polyethylene glycol 400 and water, and heating and refluxing to obtain solution A;
(2) Mixing the solution A prepared in the step (1) with ferrate, and reacting at the same temperature as in the step (1) to prepare solution B;
(3) Taking supernatant liquid of the liquid B prepared in the step (2), and marking the supernatant liquid as liquid C;
(4) Mixing the C solution and H in the step (2) 2 O 2 Mixing at room temperature, and etching by hydrogen peroxide to generate sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity, which are marked as SQDs.
2. The method for preparing the sulfur quantum dot with the simulated oxidase activity and high fluorescence quantum yield according to claim 1, wherein the mass volume ratio of sublimed sulfur, sodium hydroxide, polyethylene glycol 400 and water is 0.7g:2g:1.5mL:25mL; said H 2 O 2 The concentration of the solution C and H is 1.6-6.5 mM 2 O 2 Is equal in volume.
3. The method for preparing sulfur quantum dots with high fluorescence quantum yield and simulated oxidase activity according to claim 2, wherein the H is 2 O 2 Is 4mM.
4. The method for preparing the sulfur quantum dots with the simulated oxidase activity and high fluorescence quantum yield according to claim 1, wherein the mass ratio of sublimated sulfur to ferrate is 21.875:0.151.
5. the method for preparing the sulfur quantum dot with the simulated oxidase activity and high fluorescence quantum yield according to claim 1, wherein the temperature of the heating reflux is 70 ℃.
6. A sulfur quantum dot prepared by the preparation method of any one of claims 1 to 5.
7. Use of the sulfur quantum dot of claim 6 for preparing an antibacterial agent for inhibiting drug-resistant escherichia coli and/or methicillin-resistant staphylococcus aureus.
8. Use of the sulfur quantum dot of claim 6 for detecting folic acid in non-diagnosis.
9. A method of using the sulfur quantum dot of claim 6 for detecting folic acid in non-diagnosis, comprising:
and adding the sulfur quantum dots into a sample to be detected, reacting at pH of 2-11, and measuring the fluorescence intensity of the reaction liquid at 450 nm.
10. The method for detecting folic acid in non-diagnosis by sulfur quantum dot according to claim 9, wherein the pH is 7-11 and the reaction time is 1-10 minutes.
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